Effect of column flexural capacities and axial loads on bond behavior of interior beam-column joints

Abstract

The bond behavior of longitudinal beam bars passing through the joint zone is affected by the column flexural capacity, while there is a paucity of research results; in addition, the bond behavior can be improved by the axial compressive load, while the upper limit of the axial load was still not clear due to lack of experimental researches with high axial load ratios (larger than 0.6). In this investigation, the hysteretic behavior of 8 interior joints with 600 MPa high-strength longitudinal beam reinforcing bars was compared and analyzed in detail. Four joints adopted the concrete-filled steel tubular column with continuous steel tube, namely CFSTJ specimens; and the other four joints, i.e., their counterparts, adopted the concrete-filled steel tubular column with discontinuous steel tube, namely TRCJ specimens. The discontinuous column steel tube led to different column flexural capacities and axial load ratios. The test results showed that all specimens exhibited good hysteretic behavior before 5% drift, and the bond behavior of CFSTJ specimens was better than that of their counterpart TRCJ specimens. Combining these observations with available test data of reinforced concrete (RC) interior joints in the literature, the effect of column flexural capacities and axial loads on the bond behavior was then further analyzed and quantified. Finally, based on provisions in NZS 3101 and EN 1998–1, more accurate design equations were proposed by considering the depth of column compression zone and limiting the axial load ratio.